LN2 Safety

When it comes to cryogenics, safety is our number one priority. Here is an inside look into how we educate on cool fuel safety:

Week 1: LN2 Safety & Ice Cream Workshop

Lauren Reising and Justin Jessop kicked off our summer training in quite a creative way.

The workshop followed HYPER’s learn one, do one, teach one process. Each person attending was paired with another lab member. Lauren and Justin would teach the first team how to do a station, then that team would teach the next team, and so on. At each station, a simple procedure would be explained ahead of time then a discussion of the importance of the demonstration would be disused afterwards (pull style learning as opposed to push). There were a total of seven stations of the workshop, each representing a different aspect of liquid nitrogen safety.

Station 0: PPE. Personal Protective Equipment is essential to all laboratory activities and especially when working with cryogenics. The proper PPE for liquid nitrogen includes cryogenic gloves, safety glasses, non-wicking shoes (including leather, canvas, waterproof, and anything that LN2 cannot absorb into), and long pants that go over the tops of your shoes to insure that liquid nitrogen cannot go into your shoes. It is also important to remember general laboratory safety, long hair tied back and no loose clothing.

Station 1: Fill. There are a few key things to remember when filling a dewar with liquid nitrogen, including checking that everyone is wearing proper PPE., how to properly install the transfer hose, and the steps to take in order to fill the dewar. It is also important to teach some basic dewar anatomy (liquid port location, dewar level gauge, and prv location), that way participants are familiar with the supply Dewar and aren’t surprised or scared when the prv vents.

Station 2: Breaths. Asphyxiation is one of the most commonly know hazards of liquid nitrogen and other cryogenics. This is when there is not enough oxygen in the air for someone to breathe. In order to demonstrate this concept, Oxygen monitors were used. A beaker was placed inside of another container, and the Oxygen monitor was placed outside of that container. The demonstration showed that not only is air displaced inside of the beaker, but also the areas surrounding, displaying to participants the importance of proper ventilation and ensuring that nitrogen vapor won’t displace the air in a given room/space.

Station 3: Burns (Hot). When working with liquid nitrogen (77 K), liquid air (~20% oxygen and 80% nitrogen) can condense onto cold conductive surfaces due to its higher liquefaction temperature (90K). If one places LN2 into a metal beaker for example, after a few moments liquid droplets will begin to form. This is liquid air. Since there is oxygen in air, this means that part of the liquid air dripping from the flask is liquid oxygen, which is very flammable. To demonstrate this, a metal flask was placed on a stand above a separate metal container with a piece of steel wool in it. After pouring liquid nitrogen into the flask and observing the liquid air dripping onto the steel wool below, a match was then lit and placed onto the steel wool. It could be observed that even after the match had gone out, the liquid air kept the steel wool lit, pulsing red each time a droplet fell. If one considers the three sides of the fire triangle, in this case our fuel is the steel wool, our ignition is a match, and the oxygen is concentrated in liquid form.

Station 4: Burns (Cold). The other type of burn that can come from liquid nitrogen are cold burns. These occur when liquid nitrogen come into contact with your skin for a certain amount of time. To demonstrate this concept, shoes, gloves and thermocouples were used. The thermocouples wires were first placed in two shoes. One being a leather boot, and the other a tennis shoe. Liquid nitrogen was then poured over both shoes and the temperature of both were observed. The temperature of the boot only getting slightly colder (65 F), and the tennis shoe becoming extremely cold (-200 F) and visibly soaking in the liquid nitrogen. Then the same demonstration was completed on a cryogenic glove and a welding glove, similar results were seen. There is a common misconception that welding gloves can be used when handling liquid nitrogen. After completing this demonstration and seeing the temperature difference as well as the appearance of the welding glove, it is apparent that proper PPE is the only thing keeping participants safe from -200 F temperatures

Station 5: Bursts. Liquid Nitrogen Liquifies at 77 Kelvin (equivalent F temp here), Any surface or medium that is warmer than this 77 K will add heat to the nitrogen and can quickly boil it off. Nitrogen expands approximately 700 times from liquid to vapor. Keeping nitrogen in a closed vessel with no source of cooling causes rapid expansion and pressure build up, this can cause explosions. To demonstrate both the pressure build up and the explosion, liquid nitrogen was poured into a disposable plastic water bottle and a balloon was placed over the opening. participants stepped back roughly 20 feet from the bottle and observed as the balloon expanded and, after two to three minutes popped. (utilizing a metal flask with narrow mouth would likely improve this experiment to facilitate better heat transfer)

Station 6: Ice cream! Finally, we made liquid nitrogen ice cream! Each person began by mixing their ice cream base (heavy whipping cream, half & half, sugar, and vanilla extract). Then, each partner took turns pouring liquid nitrogen slowly into their partners bowl while they stirred. After about three minutes of adding LN2 and mixing, you have ice cream! It is important not to add any toppings to the ice cream until you have waited two to three minutes to ensure all of the liquid nitrogen has boiled off and it is safe to eat.

We error proofed via using smaller pyrex beakers with sharpie lines that indicated LN2 needed for each demo. by having the experience of the prior team at each station safety risks were kept to a minimum as guidance could be offered when needed. Procedures were kept at each station for reference if needed.

This workshop was a great way to kick off the summer workshops. Everyone who attended learned the main points of liquid nitrogen safety and saw that, when handled safely, liquid nitrogen is extremely useful and fun!

LN2 Safety Video: